Various kinds of pumps, such as water pumps, vacuum pumps, compressors, etc. utilize a piston to provide the pumping action. By using a double-acting piston, one piston can provide the pumping action for separate pumping chambers with the pumping chambers being operated out of phase.
Motors for driving pumps typically provide rotary output motion. It is necessary to convert the rotary output motion of the motor to a linear reciprocating driving force in order that the double-acting piston can be reciprocated. One convenient way to accomplish this is to use a rotatable drive member which may include a cam or an eccentric. With this arrangement, the rotatable drive member bears against spaced apart, opposed surfaces of the piston, and this enables rotary motion of the eccentric to linearly reciprocate the piston. Pistons of this type are shown, for example, in my prior U.S. Pat. Nos. 3,410,477 and 3,834,840.
One problem with constructions of this type is how to properly provide for contact between the rotatable drive member and the associated drive surfaces of the piston. Ideally, there should be no clearance between the peripheral surface of the rotatable drive member and the drive surfaces of the piston. If there is a very slight clearance space, even as small as 0.002 inch, wear is accelerated and noise is produced. On the other hand, if there is any significant preloading of the rotatable drive member, the rotatable drive member tends to skid on the drive surfaces of the piston, and this also accelerates wear.